Accumulation and release of mechanical energy is a phenomenon deployed in several devices. Springs are one of the commonest elements used for this purpose. Both compression as well as extension springs are made use of.
For using compression springs, pre-compression is the first pre-requisite. Pre-compression is either achieved by surfaces external to the spring or by constraining the spring modularly. The first method viz. pre-compression by external surfaces requires skillful and time consuming assembly.
The second method viz. modular constraining is described, particularly for actuators in German patent DE 9314412, a U.S. Pat. No. 8,181,947 and also in patent Application WO2010/063514. In all these, the minimum length of cartridge is fixed. So even if the spring can be compressed to the solid length, the limitation of cartridge design does not allow. Further, these methods cannot be used efficiently for varying diameter compression springs which can be otherwise compressed up to coil thickness.